Isolated cleft lip and palate is a common congenital problem with a complex etiology. The objective of this research is to identify the function of genes critical to palatal formation. Genetic variation in Interferon Regulatory Factor 6 (IRF6) causes Van der Woude syndrome (VWS) and contributes 12% risk of isolated cleft lip and palate. The pathway containing Irf6 and its cellular role in orchestrating palatal development is not known. Mice deficient for Irf6 have cleft palate, micrognathia and oral adhesions. Mice deficient for either FgflO or Tbx1 have cleft palate and oral adhesions. Mutations in Tbx,1, FgflO, and Fgf8 in humans cause cleft lip and palate. Preliminary data from our laboratory suggests that FgflO expression in the palatal mesenchyme and Fgf8 expression in the palatal epithelium may be downstream targets for Irf6 activation. Furthermore, Irf6 in the craniofacial region may modulate expression of Tbx1 in the palate. Thus, we hypothesize that Irf6 functions in both a cell-autonomous manner to regulate epithelial differentiation and in a non-cell autonomous manner affecting mesenchymal differentiation and these functions are mediated in part through the Fgf signal transduction pathway and Tbx1. We propose to establish the role of Irf6 in palatogenesis and epithelial-mesenchymal signaling. We will evaluate apoptosis and proliferation in IrfSA- palatal shelves in-vivo and using in-vitro palatal cultures. Chimeric mice will be used to determine if Irf6 signals in a cell-autonomous fashion. To identify the role of Irf6 in palatal mesenchyme development we will use neural crest and non-neural crest specific ere mouse lines. In Aim 2 we will determine if FgflO is a downstream target of Irf6 signaling during palatal growth. We will evaluate changes in Irf6 and FgflO expression in Irf6 and FgflO null mice and test if there is a direct genetic interaction by creating double Fgf10/lrf6 heterozygous mice. In Aim 3 we will identify the gene(s) responsible for Irf6 signaling from the epithelium to the mesenchyme. We will investigate changes in expression of Tbx1 and Fgf8 in lrf6-\- mice. To test whether there is a direct genetic interaction, we will create double heterozygous Irf6/Tbx1 and Irf6/Fgf8 mice. The goal of this research is to understand the signaling pathway that includes IRF6, and how defects in this pathway lead to cleft lip and palate. We will use this information to examine potential gene-gene interactions in human cleft lip and palate patients.